Method and apparatus for transmission and reception in multi-carrier wireless communication systems

ABSTRACT

Data transmission and reception is provided by configuring control channels in a wireless communication system using a plurality of carriers. User equipment (UE) may monitor physical downlink control channel (PDCCH) candidates within common search spaces (CSSs) and User Equipment-specific search spaces (USSs). If the UE is configured with cross-carrier scheduling, when two PDCCH candidates originating from a CSS and a USS, respectively, have cyclic redundancy check (CRC) scrambled by the same Radio Network Temporary Identifier (RNTI) and have a common payload size and the same first control channel element (CCE) index, the UE may interpret that only the PDCCH originating from the CSS is transmitted, thereby solving ambiguity of downlink control information (DCI) detection.

RELATED APPLICATION

This application is a continuation of PCT Application No.PCT/KR2011/004163 filed on Jun. 8, 2011, which claims priority to, andthe benefit of, Korean Patent Application No. 10-2010-0054026 filed onJun. 8, 2010, Korean Patent Application No. 10-2010-0063401 filed onJul. 1, 2010, and Korean Patent Application No. 10-2011-0054501 filed onJun. 7, 2011. The content of the aforementioned applications isincorporated by reference.

BACKGROUND

Embodiments of the present invention relate to a method and apparatusfor configuring control channels in a wireless communication systemusing a plurality of carriers, and performing transmission andreception.

A long Term Evolution (LTE) release 8 (Rel-8) user equipment (UE) inaccordance with an LTE Rel-8 standard may receive data via a singledownlink component carrier at a time. In addition, the LTE Rel-8 UE maytransmit uplink control information (UCI) via an uplink componentcarrier corresponding to the downlink component carrier.

An LTE-Advanced (A) UE in accordance with an LTE-A standard maysimultaneously receive data via a single or a plurality of downlinkcomponent carriers.

SUMMARY

An aspect of the present invention provides a user equipment (UE) and acommunication method of the UE that may solve ambiguity of downlinkcontrol information (DCI) detection.

Another aspect of the present invention provides an E-UTRAN Node-B (eNB)and a communication method of the eNB that may solve ambiguity of DCIdetection.

According to an aspect of the present invention, there is provided aLong Term Evolution (LTE)-Advanced user equipment (UE) to monitorphysical downlink control channel (PDCCH) candidates, which are cyclicredundancy check (CRC) scrambled by Radio Network Temporary Identifier(RNTI), within common search spaces (CSSs) and User Equipment-specificsearch spaces (USSs), wherein when two PDCCH candidates from a CSS and aUSS, respectively, are CRC scrambled by the same RNTI and have a commonpayload size and the same first control channel element (CCE) index, thePDCCH originating from the CSS is considered to be transmitted.

The LTE-Advanced UE may be configured to use carrier indicator field(CIF). The monitoring may mean that interpretation of each of the PDCCHcandidates is attempted based on all the monitored downlink controlinformation (DCI) formats.

The PDCCH candidates may define a search space with an aggregation levelL.

The CSS may include a total of 16 CCEs from CCE 0 to CCE 15, CCEscorresponding to an m^(th) PDCCH candidate may be given byL{(Y_(k)+m′)mod └N_(CCE,k)/L┘}+i. CCEs corresponding to an m^(th) PDCCHcandidate of a USS may be given by L{(Y_(k)+m′)mod └N_(CCE,k)/L┘}+i.

Here, i=0, . . . , L−1. N_(CCE,k) may denote a total number of CCEs.m′=m in case of the CSS. In case of the USS, when the monitoring UE isnot configured with CIF, m′=m. In case of the USS, when the monitoringUE is configured with CIF, m′=m+M^((L))·n_(CI), M^((L)) may denote thetotal number of PDCCH candidates, n_(CI) may denote the value of theCIF, m=0, . . . , M^((L))−1, and Y_(k) may correspond to zero for theCSSs and be defined for the USSs according to Y_(k)=(A·Y_(k-1))mod D.

Here, Y⁻¹=n_(RNTI)≠39827, A=39827, D=65537, k=└n_(s)/2┘, n_(s) maydenote a slot number, and n_(RNTI) may denote an RNTI value.

The CSS may correspond to a CSS with aggregation level 4 or 8.

The USS may correspond to a USS with aggregation level 1, 2, 4, or 8.

The CSS and the USS may overlap each other.

The PDCCH candidates may have a predetermined DCI format(s) and are CRCscrambled by an RNTI.

Among the PDCCH candidates, PDCCH candidates originating from the USSmay have at least one possible CIF value for the DCI format.

Among the PDCCH candidates originating from the USS, a PDCCH candidatewith a given DCI format size may be transmitted from any USScorresponding to any value of the possible CIF values for the given DCIformat size.

According to another aspect of the present invention, there is providedan LTE-Advanced eNB configured to transmit PDCCH in the CSSs and USSs,wherein when two PDCCH candidates from a CSS and a USS, respectively,are CRC scrambled by the same RNTI and have a common payload size andthe same first CCE index, only the PDCCH candidate from the CCS istransmitted.

The PDCCH candidates may define a search space with aggregation level L.

The PDCCH candidates may have a predetermined downlink controlinformation (DCI) format(s) and are CRC scrambled by an RNTI.

Among the PDCCH candidates, PDCCH candidates originating from the USSmay have at least one possible CIF value for the DCI format.

Among the PDCCH candidates originating from the USS, a PDCCH candidatewith a given DCI format size may be transmitted from any USScorresponding to any value of the possible CIF values for the given DCIformat size.

According to still another aspect, there is provided a communicationmethod of a UE, the method comprising: monitoring PDCCH candidates withCRC scrambled by an RNTI, within CSSs and USSs; and receiving PDSCH viaa plurality of downlink control carriers (CCs). The monitoring mayinclude receiving only PDCCH originating from the CSSs when the PDCCHcandidates have a common payload size and the same first CCE index. ThePDCCH candidates may have a predetermined downlink control information(DCI) format(s) and are CRC scrambled by an RNTI, the PDCCH candidatesoriginating from the USSs may have at least one possible CIF value forthe DCI format, and the plurality of downlink CCs may be identifiedbased on the CIF.

The monitoring may further include receiving PDCCH originating from theCSSs and the USSs when the PDCCH candidates have different payload sizesor different first CCE indices.

The monitoring may further include interpreting each of the PDCCHcandidates based on all the DCI formats that the UE needs to monitor.

The method may further include transmitting physical uplink sharedchannel (PUSCH) to an E-UTRAN Node-B (eNB) via a plurality of uplinkCCs.

Each of the PDCCH candidates may include at least one CCE.

An aggregation level may correspond to the number of CCEs constitutingeach of the PDCCH candidates.

A search space may be defined independently for each aggregation level.

According to embodiments of the present invention, there may be provideda user equipment (UE) and a communication method of the UE that maysolve ambiguity of downlink control information (DCI) detection.

Also, according to embodiments of the present invention, there may beprovided an E-UTRAN Node-B (eNB) and a communication method of the eNBthat may solve ambiguity of downlink control information (DCI)detection.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a table showing properties of physical downlink controlchannel (PDCCH) candidates to be monitored by a user equipment (UE)according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating a case where a common search space(CSS) and a User Equipment-specific search space (USS) corresponding toaggregation level 2 overlap each other according to an embodiment of thepresent invention;

FIG. 3 is a diagram illustrating a case where a USS corresponding toaggregation level 2 and a USS corresponding to aggregation level 4overlap each other according to an embodiment of the present invention;

FIG. 4 is a diagram illustrating a communication method of an E-UTRANNode-B (eNB) and a UE in a Long Term Evolution (LTE)-Advanced systemaccording to an embodiment of the present invention;

FIG. 5 is a diagram illustrating a case where a CSS and a USScorresponding to aggregation level 1 overlap each other according to anembodiment of the present invention;

FIG. 6 is a diagram illustrating a case where a CSS and a USScorresponding to aggregation level 2 overlap each other according to anembodiment of the present invention;

FIG. 7 is a diagram illustrating a case where a CSS and a USScorresponding to aggregation level 4 overlap each other according to anembodiment of the present invention; and

FIG. 8 is a diagram illustrating a case where a CSS and a USScorresponding to aggregation level 8 overlap each other according to anembodiment of the present invention;

DETAILED DESCRIPTION

Reference is now made in detail to embodiments of the present invention,examples of which are illustrated in the accompanying drawings, whereinlike reference numerals refer to the like elements throughout. Theembodiments are described below in order to explain the presentinvention by referring to the figures.

FIG. 1 is a table showing properties of physical downlink controlchannel (PDCCH) candidates to be monitored by a user equipment (UE)according to an embodiment of the present invention.

Hereinafter, a structure of PDCCH according to Long Term Evolution (LTE)Release-8/9 (Rel-8/9) is described.

A single PDCCH may include a single or a plurality of control channelelements (CCEs).

The number of CCEs constituting a single PDCCH may also be referred toas aggregation level.

According to a 3^(rd) Generation Partnership Project (3GPP) TechnicalSpecification (TS) Rel-8/9, a set of PDCCH candidates to be monitored bythe UE may be defined in terms of search space.

The search space may be independently defined for each PDCCH aggregationlevel. That is, PDCCH candidates may define a search space withaggregation level L. Also, the defined search spaces may overlap eachother.

According to an LTE Rel-8/9 standard, the UE may detect controlinformation delivered to the UE by monitoring common search spaces(CSSs) and User Equipment-specific search spaces (USSs).

The monitoring means that interpretation of each of PDCCH candidates isattempted based on all the downlink control information (DCI) formatsthat the UE needs to monitor.

PDCCH candidates to be monitored by the UE may be located within thesearch spaces.

If a search space corresponding to aggregation level L is denoted S_(k)^((L)), CCEs corresponding to an m^(th) PDCCH candidate of the searchspace S_(k) ^((L)) may be given by Equation 1:L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  [Equation 1]

Here, N_(CCE,k) denotes the total number of CCEs available that anE-UTRAN Node-B (eNB) can use for transmitting PDCCHs.

i=0, . . . , L−1, and m=0, . . . , M^((L))−1.

M^((L)) denotes the total number of PDCCH candidates to be monitored bythe UE in the given search space.

The UE may need to monitor a CSS for each of aggregation level 4 andaggregation level 8, and may need to monitor a USS for each ofaggregation level 1, aggregation level 2, aggregation level 4, andaggregation level 8.

The CSSs and USSs may have an overlapping area.

Also, CCEs corresponding to an m^(th) PDCCH candidate of the searchspace S_(k) ^((L)) may be given by Equation 2:L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  [Equation 2]

Here, m′=m for the CSSs.

For the USSs, when the monitoring UE is not configured with CIF, m′=m.For the USSs, when the monitoring UE is configured with CIF, for aserving cell where PDCCH is monitored, the following Equation 3 mayhold. That is, for the UE configured with CIF, the following Equation 3may hold.m′=m+M ^((L)) ·n _(CI)  [Equation 3]

Here, n_(CI) denotes the CIF value.

FIG. 1 shows Table 9.1.1-1 in 3GPP TS 36.213. The table in FIG. 1 showsaggregation levels L to be monitored by the UE, the sizes of the searchspaces with aggregation level L (in CCEs), and the number of PDCCHcandidates M^((L)) to be monitored by the UE in the search space S_(k)^((L)).

In the case of the CSSs, Y_(k) may be set to 0. Thus the CSScorresponding to aggregation level 4 and the CSS corresponding toaggregation level 8 may exactly overlap each other. That is, each CSSmay consist of a total of 16 CCEs from CCE 0 to CCE 15.

In the case of the USSs, Y_(k) may be defined by Equation 4:Y _(k)=(A·Y _(k-1))mod D  [Equation 4]

Here, Y⁻¹=n_(RNTI)≠0, A=39827, D=65537, and k=└n_(s)/2┘.

n_(s) denotes the slot number, and n_(RNTI) denotes the Radio NetworkTemporary Identifier (RNTI) value.

In the LTE-Advanced system, DCI may include carrier indicator field(CIF). The CIF may indicate which downlink CC or uplink CC is targetedby the downlink assignment information or uplink grant information.Specifically, downlink CCs may be identified based on the CIF, i.e.,based on downlink assignment information of the CIF and uplink CCs maybe identified based on uplink grant information of the CIF.

The PDCCH candidates may have a predetermined DCI format(s) and havecyclic redundancy check (CRC) scrambled by an RNTI, for example, Cell(C)-RNTI or semi-persistent scheduling (SPS) C-RNTI, and may have one ormore possible CIF values for the DCI format.

Among the PDCCH candidates originating from the USSs, a PDCCH candidatewith a given DCI format size may be transmitted from any USScorresponding to any value of the possible CIF values for the given DCIformat size.

FIG. 2 and FIG. 3 are diagrams to describe why ambiguity of DCIdetection may occur in an LTE Rel-8/9 standard not using carrieraggregation and a method of avoiding the ambiguity.

The LTE may use a circular buffer for PDCCH channel coding and ratematching. Accordingly, a codeword obtained after the channel coding maybe repeated in a circular manner.

When considering a single PDCCH including a total of M CCEs from CCE kto CCE (k+M−1), the contents of the starting CCE, which is CCE k, mayrepeat in CCE i (k<i<k+M).

In this case, if CCE i corresponds to one of the starting CCEs of a UE'sUSS with aggregation level L, when the UE attempts PDCCH detection withrespect to L CCEs from CCE i to CCE (i+L−1) with CCE i as the startingCCE, it may be possible that the detection result passes the CRC test.

In this case, the UE may recognize CCE i as the starting CCE. However,the eNB has actually transmitted CCE k as the starting CCE.

Especially, the index of the starting CCE may be used for mapping ofPUCCH acknowledgement (ACK)/negative-acknowledgement (NAK) channelresources. Accordingly, when the UE erroneously recognizes the startingCCE, it may cause erroneous mapping of ACK/NAK resources.

FIG. 2 is a diagram illustrating a case where a CSS 210 and a USS 220corresponding to aggregation level 2 overlap each other according to anembodiment of the present invention.

In a case where the CSS 210 and the USS 220 corresponding to aggregationlevel 2 are formed as shown in FIG. 2, even though an eNB actuallytransmits a PDCCH using CCE 0 through CCE 3 of the CSS 210, a UE mayattempt PDCCH detection for the shaded part 230. In this case, it may bepossible that the demodulation result for the shaded part 230 passes theCRC test.

In contrast, when the eNB transmits a PDCCH corresponding to aggregationlevel 2 using (CCE 2, CCE 3), even though the UE attempts to detect aPDCCH corresponding to aggregation level 4 with respect to CCE 0 throughCCE 3 of the CSS 210, it may be possible that the CRC test for thedetection is passed.

In the above example, “(CCE 2, CCE 3)” indicates CCE 2 and CCE 3.

FIG. 3 is a diagram illustrating a case where a USS 310 corresponding toaggregation level 2 and a USS 320 corresponding to aggregation level 4overlap each other according to an embodiment of the present invention.

In a case where an overlapping area occurs between the USS 310corresponding to aggregation level 2 and the USS 320 corresponding toaggregation level 4 as shown in FIG. 3, even though an eNB actuallytransmits a PDCCH using CCE 8 through CCE 11, that is, a PDCCHcorresponding to aggregation level 4, the UE may succeed in detecting aPDCCH corresponding to aggregation level 2 for the shaded part (CCE 10,CCE 11) 330.

In contrast, even though the eNB actually transmits a PDCCHcorresponding to aggregation level 2 using (CCE 10, CCE 11), the UE maysucceed in detecting a PDCCH corresponding to aggregation level 4 withrespect to CCE 8 through CCE 11.

In order to avoid the aforementioned problem explained by referring toFIG. 2 and FIG. 3, in LTE Rel-8/9, the contents of CCE k correspondingto the starting CCE is not allowed to be repeated in other subsequentCCEs.

Specifically, a single CCE may transmit a total of 72 bits. Also,tail-biting convolutional coding with a coding rate of ⅓ may be used forPDCCH encoding. Information may go through 16-bit CRC coding beforebeing input to a channel encoder.

The basic output length of the channel encoder may be 3×(payloadsize+16) bits. The bits may sequentially fill in a number of CCEscorresponding to the aggregation level of PDCCH.

That is, when a PDCCH transmits a length longer than the basic length,the contents of the basic length may be sequentially repeated.

Further details of the method for preventing the aforementionedrepetition are disclosed in 3GPP TS 36.212 5.1.4.2.

Considering that the aggregation level 8 for the CSS is the maximumaggregation level, that is, considering that a single PDCCH may use upto 8 CCEs, a set of payload sizes having ambiguity may be expressed byEquation 5:{a>0|common multiple(3×(a+16),72)<72×8}  [Equation 5]

Excluding the payload sizes which are not used in the specificationbecause they are too short or too long, the payload sizes havingambiguity are given in Table 1. Table 1 corresponds to Table 5.3.3.1.2-1in 3GPP TS 36.212.

That is, Table 1 shows payload sizes causing ambiguity.

The payload sizes of Table 1 are not used in the LTE Rel-8/9 since thecontents of the starting CCE may repeat in a subsequent CCE(s) withthose payload sizes.

TABLE 1 {12, 14, 16, 20, 24, 26, 32, 40, 44, 56}

In the following, the embodiment of FIG. 2 is reviewed for the casewhere the aforementioned method is applied.

In a case where the eNB actually transmits a PDCCH using CCE 0 throughCCE 3 of the CSS 210, even though the UE attempts PDCCH detection forthe shaded part 230, a case where the demodulation result for the shadedpart 230 passes the CRC test may rarely occur. That is, the demodulationresult for the shaded part 230 may pass the CRC test at a usualundetected error rate.

In addition, when the eNB transmits a PDCCH corresponding to aggregationlevel 2 using (CCE 2, CCE3) of the USS 220, and when the UE attempts todetect a PDCCH corresponding to aggregation level 4 with respect to CCE0 through CCE 3 of the CSS 210, the demodulation result with respect toCCE 0 through CCE 3 may pass the CRC test at a usual undetected errorrate.

The aforementioned description may be similarly applicable to theembodiment of FIG. 3.

According to the LTE Rel-8/9 standard, DCI formats 0, 1, 1A, 1B, 1D, 2,2A, and 2B may be CRC scrambled by a C-RNTI. These DCI formats can betransmitted in the USSs. The DCI formats 0 and 1A may be alsotransmitted in the CSSs.

The DCI formats 0, 1, 1A, 2, 2A, and 2B may be CRC scrambled by an SPSC-RNTI, and may be transmitted in the USSs. The DCI formats 0 and 1A maybe also transmitted in the CSSs.

The DCI formats 0, 1, and 1A may be CRC scrambled by a temporary C-RNTI.In this case, the DCI format 0 may be transmitted in the CSSs and theDCI format 1 may be transmitted in the USSs, and the DCI format 1A maybe transmitted in both the CSSs and the USSs.

Because of the aforementioned reasons described above with reference toFIG. 2 and FIG. 3, all the DCI formats, for example, the DCI formats 1,1A, 1B, 1D, 2, 2A, and 2B, which are transmitted in the USSs and areassociated with downlink resource allocation, may avoid transmissionwith the payload sizes shown in Table 1.

In LTE-Advanced Rel-10 standard and later versions, the ambiguity ofPDCCH detection may be avoided by applying the above scheme for all theDCI formats (i.e., the existing DCI formats of Rel-8/9 and newly definedDCI formats) that are transmitted in the USSs and are used for downlinkresource allocation.

FIG. 4 is a diagram to describe a communication method of an eNB 410 anda UE 400 in an LTE-Advanced system according to an embodiment of thepresent invention.

In operation 420, the UE 400 may monitor PDCCH search spaces.

A PDCCH may transmit DCI information which is downlink assignmentinformation or uplink grant information.

That is, the UE 400 may be configured to monitor PDCCH candidates withCRC scrambled by an RNTI and the like, within CSSs and USSs.

In operation 430, the eNB 410 may transmit physical downlink sharedchannel (PDSCH) to the UE 400 via a plurality of downlink CCs.

In operation 440, the UE 400 may transmit physical uplink shared channel(PUSCH) to the eNB 410 via a plurality of uplink CCs.

The PDCCH search spaces to be monitored by the UE 400 may be dividedinto CSSs and USSs.

The USSs may be defined for each CC. For example, when the UE 400 isconfigured to use N downlink CCs, the UE 400 may have N individual USSsets.

When the UE 400 does not use cross-carrier scheduling, search spaces maybe defined on each CC.

When the UE 400 uses cross-carrier scheduling, a plurality of searchspace sets may be defined on a single CC. For example, two USS setscorresponding to two CCs may be defined within a single CC.

The CSS size may be configured to be the same, regardless of the numberof downlink CCs configured for the UE 400. For example, the CSS mayinclude 16 CCEs from CCE 0 through CCE 15 as in LTE Rel-8/9.

The CSS size may be configured to vary depending on the number ofdownlink CCs configured for the UE 400. In this case, the size of theCSS may be configured to increase with an increase in the number ofconfigured CCs.

Hereinafter, the ambiguity of DCI detection that may occur due tocross-carrier scheduling is described. Specifically, a CSS and USSconfiguration method of the UE 400 using cross-carrier scheduling isdescribed and a method of solving the ambiguity of DCI detection isdescribed.

In the following description, it may be assumed that the method ofavoiding the ambiguity of DCI detection in LTE, described in the abovewith reference to FIG. 2 and FIG. 3, is applied to an LTE-Advancedsystem.

For the UE 400 using cross-carrier scheduling, the eNB 410 may includeCIF within DCI formats transmitted in the USSs. The eNB 410 may informthe UE 400 of which CC is scheduled for the UE using the CIF value. ADCI format to be transmitted in the CSSs may not have CIF. A DCI formattransmitted in the USS of the UE 400 using cross-carrier scheduling maygenerally have CIF.

16 bit CRC may be added to DCI transmitted by PDCCH. When 16 bits of CRCis added, CRC scrambling may be performed using an RNTI.

The DCI format 0 and the DCI format 1 A may be CRC scrambled by a C-RNTIor an SPS C-RNTI. The DCI format 0 and the DCI format 1A may betransmitted in a CSS or USS.

DCI transmitted in the CSSs may not include CIF. DCI that is transmittedonly in the USSs and is scrambled by the C-RNTI or the SPS C-RNTI mayinclude CIF at all times.

First DCI that is transmitted only in the USSs and is scrambled by theC-RNTI or the SPS C-RNTI, and second DCI that is transmitted only in theCSSs and is CRC scrambled by the C-RNTI or the SPS C-RNTI may have thesame payload size. Also, an overlapping area may occur between the CSSsand the USSs.

In an area where search spaces overlap each other, even though the UE400 succeeds in PDCCH detection, the UE 400 may not be able to determinewhich format between the two DCI formats having the same payload size isactually transmitted. Here, that the UE 400 has succeeded in the PDCCHdetection means that the information bits obtained by the UE 400 afterperforming PDCCH demodulation and decoding have passed the CRC test.

The aforementioned issue that the UE 400 may not be able to determinewhich DCI format is transmitted may occur only when two DCI formatsoriginating from a CSS and a USS, respectively, are scrambled by thesame RNTI and have the same payload size in the overlapping area betweenthe CSS and the USS.

The DCI format 0 and the DCI format 1A may be transmitted in the CSS andthe DCI format 0 and the DCI format 1 A may have the same payload size.If a USS DCI format, among the USS DCI formats to be monitored by the UE400, has the same payload size and is CRC scrambled by the same RNTI,for example, a C-RNTI or an SPS C-RNTI as the DCI format 0 and the DCIformat 1A originating from the CCS, the aforementioned issue may occur.

The above cases where the UE 400 may not be able to determine which DCIformat is transmitted may be examined by classifying them into thefollowing cases 1) through 4):

Case 1) where a CSS and a USS corresponding to aggregation level 1overlap each other;

Case 2) where a CSS and a USS corresponding to aggregation level 2overlap each other;

Case 3) where a CSS and a USS corresponding to aggregation level 4overlap each other; and

Case 4) where a CSS and a USS corresponding to aggregation level 8overlap each other.

The CSS size may be designed to change depending on the number ofdownlink CCs configured for the UE 400. Solutions to be described belowmay assume that the structure and the size of the CSSs is the same asthe structure and the size of the CSSs used in the LTE Rel-8/9. However,the solutions may also be applicable to CSSs having different structuresand sizes.

FIG. 5 is a diagram illustrating a case where a CSS 510 and a USS 520corresponding to aggregation level 1 overlap each other according to anembodiment of the present invention.

When the UE 400 attempts detection with respect to CCE 4, the UE 400 maysuccessfully demodulate a PDCCH.

However, the UE 400 may not be able to determine from which search spacebetween the CSS 510 and the USS 520 the detected DCI originates.Accordingly, even though the UE 400 successfully detects the PDCCH, aproblem may occur in interpreting the contents of the DCI format.

In contrast, even though the UE 400 attempts to detect a PDCCHcorresponding to aggregation level 4 with respect to CCE 4 through CCE 7and thereby succeeds in the PDCCH detection, the UE 400 may not be ableto determine from which search space between the CSS 510 and the USS 520the detected DCI originates.

FIG. 6 is a diagram illustrating a case where a CSS 610 and a USS 620corresponding to aggregation level 2 overlap each other according to anembodiment of the present invention.

The UE 400 may attempt detection with respect to (CCE 4, CCE 5) andthereby may succeed in PDCCH demodulation.

However, even though the UE 400 successfully demodulates the PDCCH, theUE 400 may not be able to determine from which search space between theCSS 610 and the USS 620 the detected DCI originates. Accordingly,regardless of the UE 400 succeeding in the PDCCH detection, a problemmay occur in interpreting the contents of the DCI format. The sameproblem may also occur for (CCE 8, CCE 9) and (CCE 12, CCE 13).

In contrast, even though the UE 400 attempts to detect a PDCCHcorresponding to aggregation level 4 with respect to CCE 4 through CCE7, CCE 8 through CCE 11, or CCE 12 through CCE 15 and thereby succeedsin the PDCCH detection, the UE 400 may not be able to determine fromwhich search space between the CSS 610 and the USS 620 the detected DCIoriginates.

FIG. 7 is a diagram illustrating a case where a CSS 710 and a USS 720corresponding to aggregation level 4 overlap each other according to anembodiment of the present invention

The same problem described above with reference to FIG. 5 and FIG. 6 mayalso occur for CCE 12 through CCE 15.

FIG. 8 is a diagram illustrating a case where a CSS 810 and a USS 820corresponding to aggregation level 8 overlap each other according to anembodiment of the present invention

The same problem described above with reference to FIG. 5 and FIG. 6 mayalso occur for CCE 8 through CCE 15.

Hereinafter, the description made above with reference to FIG. 5 throughFIG. 8 is summarized. When the UE 400 attempts PDCCH detection byemploying, as the starting CCE, one of the possible starting CCEs, forexample, CCE 0, CCE 4, CCE 8, or CCE 12, of the CSS 510, 610, 710, or810 in an area where the CSS 510, 610, 710, or 810, and the USS 520,620, 720, or 820 overlap each other, a problem may occur in interpretingDCI detected by the UE 400.

Therefore, to solve the above problem, when the UE 400 attemptsdetection by employing, as the starting CCE, CCE 0, CCE 4, CCE 8, or CCE12 in the overlapping area between the CSS and the USS, a constraint maybe applied so that the detected DCI may be interpreted to originate fromthe CSS or the USS at all times.

Hereinafter, description is made about a constraint in which thedetected DCI is interpreted to originate from the CSS. The aboveconstraint may be defined by 1) and 2):

1) When the eNB 410 transmits the DCI, the eNB 410 may transmit the DCIin the CSS without any constraint; and

2) In the overlapping area between the CSS and the USS, the eNB 410 maytransmit USS DCI only when the starting CCE of DCI originating from theUSS does not correspond to any of the possible starting CCEs, forexample, CCE 0, CCE 4, CCE 8, and CCE 12 of CSS PDCCH candidates.

Compared to the scheme allowing only DCI transmission originating fromthe CSS for the whole overlapping area between the CSS and the USS, theabove scheme may have an advantage in that USS DCI may be transmitted insome parts of the overlapping area.

When the above constraint is applied to the USS corresponding toaggregation level 4 or USS corresponding to aggregation level 8, the DCItransmission originating from the USS may not be allowed in theoverlapping area between the CSS and the USS. This is because thestarting CCE of a PDCCH candidate of the USS always corresponds to astarting CCE of a PDCCH candidate of the CSS.

However, even though the above constraint is applied to the USScorresponding to aggregation level 1 or the USS corresponding toaggregation level 2, a CCE not overlapping with the starting CCEs of thePDCCH candidates of the CSS may be present in the USS corresponding toaggregation level 1 or in the USS corresponding to aggregation level 2.Accordingly, when the starting CCE does not correspond to one ofpossible starting CCEs of the CSS DCI, the USS DCI may be transmittedeven in the overlapping area between the CSS and the USS.

For example, in FIG. 5, each of CCE 2, CCE 3, CCE 5, CCE 6, and CCE 7excluding CCE 4 may be a valid PDCCH candidate of the USS. In addition,in FIG. 6, (CCE 2, CCE 3), and (CCE 6, CCE 7) may be valid PDCCHcandidates of the USS.

Alternatively, in the overlapping area between the CSS and the USS, whenthe UE 400 attempts detection by employing, as the starting CCE, CCE 0,CCE 4, CCE 8, or CCE 12, a constraint may be applied so that a detectedDCI is to be interpreted to originate from the USS at all times.

That is, when the eNB 410 transmits DCI, and when the starting CCEcorresponds to one of the possible starting CCEs of the CSS PDCCHcandidates, for example, CCE 0, CCE 4, CCE 8, and CCE 12 in theoverlapping area of the CSS and the USS, the eNB 410 may transmit onlyUSS DCI. In this case, the UE 400 may consider only the USS DCI istransmitted in the overlapping area between the CSS and the USS indetecting and interpreting a PDCCH.

Summarizing the aforementioned description, the following two methods(1) and (2) may be employed.

(1) In the overlapping area between the CSS and the USS, the UE 400 mayinterpret a PDCCH, which is considered to have DCI format ambiguity, asa CSS DCI format. That is, when PDCCH candidates have a common payloadsize and the same first CCE index, the eNB 410 may transmit only a PDCCHfrom the CSS and the UE 400 may interpret or consider that only thePDCCH from the CSS is transmitted. In this example, PDCCH candidatesfrom the CSS may be referred to as first PDCCH candidates and PDCCHcandidates from the USS may refer to as second PDCCH candidates. Whenthe first PDCCH candidates and the second PDCCH candidates have a commonpayload size and the same first CCE index, the UE 400 may determine thata PDCCH among the first PDCCH candidates is transmitted.

(2) In the overlapping area between the CSS and the USS, the UE 400 mayinterpret, a PDCCH, which is considered to have DCI format ambiguity, asa USS DCI format.

Hereinafter, methods of fundamentally removing the ambiguity of DCIdetection, different from the aforementioned (1) and (2) are described.

1) As a first method, different scrambling sequences may be applied tothe whole payload for the CSS DCI format and the USS DCI format.

The payload may include information bits and 16 bit CRC. When CRC isgenerated for information bits, the payload may be generated by addingthe generated CRC to the information bits. Bit-level scrambling may beapplied to the whole generated payload. Even though the bit-levelscrambling may be applied in the same form as in the 3GPP standard TS36.211 v 8.7.0 6.3.1, different initialization values c_(init) for thescrambling sequence generator may need to be applied for the CSS DCIformats and the USS DCI formats.

Since the initialization values for the scrambling sequence generatorare different for CSS DCI formats and USS DCI formats, the CSS DCIformats and the USS DCI formats may be scrambled by different scramblingsequences. Therefore, the UE 400 may be able to determine which DCIformat is transmitted.

2) As a second method, cyclic shifts with different offsets for the CSSDCI format and the USS DCI format can be applied for the bit stream ofthe whole payload.

That is, when the bit stream of the payload of the DCI format is “x(1),x(2), . . . x(N)”, x(i) may be changed to x((i+q) mod N)) by applyingoffset q(0<q<N) to the bitstream. Here, x(i) denotes the i^(th) bit. Forexample, if q=3, the bit order may be changed to x(4), x(5), . . . x(N),x(1), x(2), x(3).

If the offset value of the CSS DCI format and the offset value of theUSS DCI format are set to be different, the UE 400 may be able todetermine which format is transmitted.

3) As a third method, CRC scrambling may be performed by applyingdifferent RNTIs for the CSS DCI format and the USS DCI format. Ifdifferent RNTIs are allocated and are used for the CSS DCI format andthe USS DCI format, ambiguity between the CSS DCI format and the USS DCIformat may not occur.

4) As a fourth method, the payload size of the CSS DCI format and thepayload size of the USS DCI format may be maintained to be differentfrom each other at all times. For example, the CSS DCI format and theUSS DCI format may have different payload sizes by applying bit padding.

The above-described exemplary embodiments of the present invention maybe recorded in computer-readable media including program instructions toimplement various operations embodied by a computer. The media may alsoinclude, alone or in combination with the program instructions, datafiles, data structures, and the like. Examples of computer-readablemedia include magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD ROM disks and DVDs;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and perform program instructions, suchas read-only memory (ROM), random access memory (RAM), flash memory, andthe like. Examples of program instructions include both machine code,such as produced by a compiler, and files containing higher level codethat may be executed by the computer using an interpreter. The describedhardware devices may be configured to act as one or more softwaremodules in order to perform the operations of the above-describedexemplary embodiments of the present invention, or vice versa.

Although a few exemplary embodiments of the present invention have beenshown and described, the present invention is not limited to thedescribed exemplary embodiments. Instead, it would be appreciated bythose skilled in the art that changes may be made to these exemplaryembodiments without departing from the principles and spirit of theinvention, the scope of which is defined by the claims and theirequivalents.

The invention claimed is:
 1. A user equipment (UE) comprising: a monitorconfigured to monitor Physical Downlink Control Channel (PDCCH)candidates in Common Search Space (CSS) and User equipment-specificSearch Space (USS); and a receiver configured to consider a PDCCHcandidate in the CSS as PDCCH transmitted from a base station in casethat the PDCCH candidate in the CSS and a PDCCH candidate in the USShave: (1) Cyclic redundancy check (CRC) scrambled by a Radio NetworkTemporary Identifier (RNTI), (2) a common payload size, (3) a same firstControl Channel Element (CCE) index, and (4) different Downlink ControlInformation (DCI) configurations.
 2. A user equipment (UE) comprising: amonitor configured to monitor Physical Downlink Control Channel (PDCCH)candidates in Common Search Space (CSS) and User equipment-specificSearch Space (USS); configured with carrier indicator field (CIF)associated with monitoring the PDCCH candidates; and a receiverconfigured to consider a PDCCH candidate in the CSS as PDCCH transmittedfrom a base station in case that the PDCCH candidate in the CSS and aPDCCH candidate in the USS have: (1) Cyclic redundancy check (CRC)scrambled by a Radio Network Temporary Identifier (RNTI), (2) a commonpayload size, (3) a same first Control Channel Element (CCE) index, and(4) different Downlink Control Information (DCI) configurations.
 3. Auser equipment (UE) comprising: a monitor configured to monitor PhysicalDownlink Control Channel (PDCCH) candidates in Common Search Space (CSS)and User equipment-specific Search Space (USS); and a receiverconfigured to consider a PDCCH candidate in the CSS as PDCCH transmittedfrom a base station in case that the PDCCH candidate in the CSS and aPDCCH candidate in the USS have Cyclic redundancy check (CRC) scrambledby a Radio Network Temporary Identifier (RNTI), a common payload size, asame first Control Channel Element (CCE) index, and different DownlinkControl Information (DCI) configurations and in case that the PDCCHcandidate in the USS has carrier indicator field (CIF).
 4. A userequipment (UE) comprising: a monitor configured to monitor PhysicalDownlink Control Channel (PDCCH) candidates in Common Search Space (CSS)and User equipment-specific Search Space (USS), and a receiverconfigured to consider a PDCCH candidate in the CSS as PDCCH transmittedfrom a base station or consider a PDCCH candidate in the USS as PDCCHtransmitted from the base station according to predeterminedconfiguration between the base station and the UE in case that the PDCCHcandidate in the CSS and the PDCCH candidate in the USS have: (1) Cyclicredundancy check (CRC) scrambled by a Radio Network Temporary Identifier(RNTI), (2) a common payload size, (3) a same first Control ChannelElement (CCE) index, and (4) different Downlink Control Information(DCI) configurations.
 5. The UE of claim 4, wherein the RNTI is C-RNTI(Cell-RNTI) or SPS C-RNTI (Semi-Persistent Scheduling Cell-RNTI).
 6. TheUE of claim 4, wherein the PDCCH candidates belong to a search spacewith aggregation level L.
 7. The UE of claim 4, wherein the CSScomprises a total of 16 CCEs from CCE 0 to CCE 15, and CCEscorresponding to an m^(th) PDCCH candidate of a search space withaggregation level L in subframe k are given by Equation 1,L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  [Equation 1] where N_(CCE,k)denotes a total number of CCEs in subframe k, i=0, . . . , L−1. If theUE is configured with CIF, m′=m+M^((L))·n_(CI), where n_(CI) denotes avalue of the CIF, and if the UE is not configured with CIF, m′=m, wherem=0, . . . , M^((L))−1. M^((L)) denotes a number of PDCCH candidates inthe search space. Y_(k) corresponds to zero in the CSS and is defined inthe USS according to Equation 2,Y _(k)=(A·Y _(k-1))mod D  [Equation 2] where Y⁻¹=n_(RNTI)≠0, A=39827,D=65537, k=└n_(s)/2┘, n_(s) denotes a slot number, and n_(RNTI) denotesan RNTI value.
 8. The UE of claim 4, wherein: the CSS corresponds to aCSS with aggregation level 4 or 8, and the USS corresponds to a USS withaggregation level 1, 2, 4, or
 8. 9. The UE of claim 4, wherein the CSSand the USS overlap each other.
 10. The UE of claim 4, wherein: forPDCCH candidates with a given DCI format size with CIF and CRC scrambledby C-RNTI, where the PDCCH candidates have at least one possible CIFvalue for the given DCI format size, the UE assumes that a PDCCHcandidate with the given DCI format size may be transmitted from any USScorresponding to any value of the possible CIF values for the given DCIformat size.
 11. A base station comprising: a transmitter fortransmitting Physical Downlink Control Channel (PDCCH) to a userequipment (UE), wherein the base station transmits PDCCH correspondingto a PDCCH candidate in Common Search Space (CSS) to the user equipmentin case that the PDCCH candidate in the CSS and a PDCCH candidate inUser equipment-specific Search Space (USS) for PDCCH detection in theuser equipment have: (1) Cyclic redundancy check (CRC) scrambled by aRadio Network Temporary Identifier (RNTI), (2) a common payload size,(3) a same first Control Channel Element (CCE) index, and (4) differentDownlink Control Information (DCI) configurations.
 12. The base stationof claim 11, wherein the RNTI is a Cell-RNTI or a Semi-PersistentScheduling (SPS) RNTI.
 13. The base station of claim 11, wherein thePDCCH candidates belong to a search space with aggregation level L. 14.The base station of claim 11, wherein the CSS comprises a total of 16CCEs from CCE 0 to CCE 15, and CCEs corresponding to an m^(th) PDCCHcandidate of a search space with aggregation level L in subframe k aregiven by Equation 1,L{(Y _(k) +m′)mod └N _(CCE,k) /L┘}+i  [Equation 1] where N_(CCE,k)denotes a total number of CCEs in subframe k, i=0, . . . , L−1. If theUE is configured with CIF, m′=m+M^((L))·n_(CI), where n_(CI) denotes avalue of the CIF, and if the UE is not configured with CIF, m′=m, wherem=0, . . . , M^((L))−1. M^((L)) denotes a number of PDCCH candidates inthe search space. Y_(k) corresponds to zero in the CSS and is defined inthe USS according to Equation 2,Y _(k)=(A·Y _(k-1))mod D  [Equation 2] where Y⁻¹=n_(RNTI)≠0, A=39827,D=65537, k=└n_(s)/2┘, n_(s) denotes a slot number, and n_(RNTI) denotesan RNTI value.
 15. The base station of claim 11, wherein for PDCCHcandidates with a given DCI format size with CIF and CRC scrambled byC-RNTI, where the PDCCH candidates have at least one possible CIF valuefor the given DCI format size, a PDCCH candidate with the given DCIformat size can be transmitted from any USS corresponding to any valueof the possible CIF values for the given DCI format size.